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Combating eutrophication requires changes in land and water management in agricultural catchments and implementation of mitigation measures to reduce phosphorus (P), nitrogen (N) and suspended sediment (SS) losses. To date, such mitigation measures have been built in many agricultural catchments, but there is a lack of studies evaluating their effectiveness. Here we evaluated the effectiveness of mitigation measures in a clay soil-dominated headwater catchment by combining the evaluation of long-term and high-frequency data with punctual measurements upstream and downstream of three mitigation measures: lime-filter drains, a two-stage ditch, and a sedimentation pond. Long-term hydrochemical data at the catchment outlet showed a significant decrease in P (−15%) and SS (−28%) and an increase in nitrate nitrogen (NO₃–N, +13%) concentrations. High-frequency (hourly) measurements with a wet-chemistry analyzer (total and reactive P) and optical sensor (NO₃–N and SS) showed that the catchment is an abundant source of nutrients and sediments and that their transport is exacerbated by prolonged drought and resuspension of stream sediments during storm events. Lime-filter drains showed a decrease in SS by 76% and total P by 80% and an increase in NO₃–N by 45% compared with traditional drains, potentially indicating pollution swapping. The effectiveness of two-stage ditch and sedimentation pond was less evident and depended on the prevalent hydrometeorological conditions that drove the resuspension of bed sediments and associated sediment-bound P transport. These results suggest that increased frequency of prolonged drought due to changing weather patterns and resuspension of SS and sediment-bound P during storm events can override the generally positive effect of mitigation measures.

Reducing eutrophication requires large financial investments that can be for example used to support catchment stakeholders in building agri-environment mitigation measures. These measures aim at reducing nutrient and sediment losses from agricultural land to recipient waters. In recent years, a large number of studies has looked into their effectiveness and generally show that some measures are successful and others fail to deliver expected improvements in water quality, which is increasingly difficult to communicate to stakeholders expecting immediate results. Particularly, transport mitigation measures that aim at intercepting stream or drainage flow, can have a varying effectiveness. Two measures of the same type and built in a seemingly similar way can have completely opposite impact on water quality, depending on the local catchment properties. In this paper we examine factors controlling effectiveness of mitigation measures looking at their hydrochemical positioning in the catchment in relation to pollution sources including nutrient legacy sources, their hydrochemical behaviour, design, management and stakeholders’ engagement, using examples for transport mitigation measures: constructed wetlands, sedimentation ponds, two-stage ditches and drainage filters. We discuss also typical trade-offs in attainment of different ecosystem services which catchment stakeholders should consider prior to selecting and building the measures, including pollution swapping mechanisms e.g. reducing P-controlled eutrophication but increasing N-controlled eutrophication or reducing eutrophication vs. increasing greenhouse gas emissions. We show also how increasing weather variability and nutrient saturation can lead to further deterioration in water quality despite implementation of measures, making mitigation efforts ineffective under changing climate and in catchments with nutrient legacy sources.

The paper presents the results of a scientific project focused on limiting nutrient losses from farms by introducing measures to apply fertilizers in a more sustainable way. It is a case study of selected aspects of farm management, focussing on the issue of sustainable agriculture and their tools. The main aim of the study was to analyse and evaluate farmers’ knowledge of the fertilizing process and its aspects, as well as applying sustainable agricultural activities on farms. The study emphasised the importance of nutrient management, as very important for sustainable farming. Also, the links between farmers’ opinions and their activities were analysed. The important issue concerned measures for sustainable farm management introduced on the farms, as well as measures to limit nutrient leaching into groundwater. Twenty-eight farmers from two regions in Poland were interviewed about their perceptions for the case study. In general, the farmers considered their farm activities to be more sustainable than in the past. They demonstrated an understanding of the general idea of sustainable agriculture. However, many farmers still demonstrated a poor grasp of nutrient flows and nutrient balances on farms. Their knowledge and perception was based on general, rather than specific knowledge gleaned from an academic/vocational course. The farmers demonstrated a realization that there were some new, or low-cost measures that could be introduced to make management more sustainable and pro-environmental, but there was still a need for wider adoption of sustainable agricultural practices.

To improve understanding of phosphorus (P) retention processes in small constructed wetlands (CWs), we analysed variations in sediment deposition and accumulation in four CWs on clay soils in east-central Sweden. Sediment deposition (in traps) generally exceeded the total suspended solids (TSS) load suggesting that resuspension and wetland base erosion were important. This was confirmed by quantification of particle accumulation (on plates) (1–23 kg m−2 year−1), which amounted to only 13–23% of trap deposition. Spatial mean P concentrations in accumulated sediment on plates (0.09–0.15%) were generally similar to temporal mean P concentrations of particles in water (0.11–0.15%). Deposition/accumulation was minor in one wetland with high hydraulic load (400 m year−1), suggesting that such small wetlands are not efficient as particle sinks. Economic support for CWs are given, but design and landscape position are here demonstrated to be important for effective P retention. Electronic supplementary material The online version of this article (10.1007/s13280-017-0992-9) contains supplementary material, which is available to authorized users.

Raising environmental awareness among farmers is the key to successfully reaching environmental goals. The present study assessed the knowledge development process and the raising of environmental awareness among 30 farmers from Poland exposed to four approaches aimed to reduce phosphorus (P) and nitrogen (N) losses to water. The farmers were interviewed with open-ended questions on-farm both before and after the project intervention. As hoped, the farmers attempted to adjust their farm practices to the European Union regulations, which are in some cases supported by subsidies. As a complement, the project offered tools for system-thinking based on farm data and support from agricultural advisors: a) a survey of plant-available P, potassium (K), magnesium (Mg), and soil pH, resulting in soil maps; b) assessment of nitrogen leaching risks from individual fields; c) compilation of a farm-gate balance. Farmers were positive to soil surveys and maps, but had limited understanding of the nutrient balance concept and calculations. They generally relied on their own experiences regarding fertilization rather than on calculated farm nutrient balances and leaching risks. Farmers’ understanding and willingness to adopt new approaches to improve nutrient efficiency and reduce negative environmental impacts are discussed.

Horse paddocks have been identified as a significant contributor of animal waste nutrients to natural waters; thus, modified paddock management is needed. Because chemical amendments pose a health risk to horses, an alternative for reducing nutrient translocation from manure is to add available organic residues to the soil. To examine the feasibility of outdoor use of organic materials to reduce nutrient losses from paddock soils, three commonly available organic materials (peat, wheat straw, and wood chips) were tested for their nutrient retention capacities in batch experiments followed by leaching experiments in an in-house lysimeter station using artificial rainfall. Results showed that the grounded peat and wood chips retained some phosphorus (P), whereas grounded wheat straw released P to the solution. In leaching experiments, peat reduced nitrogen (N) losses by 40% but increased P and carbon (C) losses severalfold. Wheat straw was ineffective in reducing P, N, or C losses and in some cases increased the losses. Wood chips effectively reduced P and C losses, by 70 and 40%, respectively, but not N losses. It was concluded that, among the three organic materials, only the wood chips can be used outdoors to reduce nutrient losses from paddock soils.

The winter climate in northwestern Europe is commonly influenced by the North Atlantic Oscillation (NAO). Its intensity, expressed as an index (NAO), has been suggested for use in assessing nutrient leaching from arable land to water and the effects of mitigation measures. We found significant ( < 0.05) positive linear relationships between NAO and an air freezing-thawing index in central and southern Sweden for 2004 to 2016. This period covered winters with both extreme low and high NAO. There were significant negative linear relationships between NAO and a snow depth index. Management and nutrient leaching were studied simultaneously in two agricultural catchments (20.7 ha, code 11M; 788 ha, code M36) in southwestern Sweden. Catchments 11M (silty-clay soil) and M36 (sandy hills with a central, heavy clay plain) are both artificially drained. Total N and total P leaching increased significantly with winter (November-April) NAO in both catchments. In contrast, leaching of dissolved reactive P (DRP) was not related to NAO. The highest DRP concentrations were observed in connection with specific agricultural practices, whereas moderately elevated DRP concentrations were linked to snowmelt events. Concentrations of P in other forms (other P) were even more elevated (1.02 mg L) in 11M in winter 2014-2015, probably due to a large (32% of area) internal buffer (ley-fallow) in a central ravine being plowed down in autumn 2014. No general trend in P or N fertilization was found in catchment M36. Thus NAO may be appropriate for use in trend analyses of nutrient load in the study region.

Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (o ≥ 0.3 mm) in soil columns and mesopores (o ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (e>1.0 mm) and medium sized macropores (e0.3–1.0 mm) towards smaller macropores (e0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space.

With time, different soil-forming processes such as weathering, plant growth, accumulation of organic matter, and cultivation are likely to affect phosphorus (P) speciation. In this study, the depth distribution of P species was investigated for an agricultural clay soil, Lanna, Sweden. Small amounts of apatite-P was demonstrated in the topsoil whereas the speciation of Pat 70-100 cm depth consisted of approximately 86% apatite according to P K-edge XANES (X-ray absorption near-edge structure) spectroscopy. Because there were only minor differences in bulk mineralogy and texture, these variations in P speciation were interpreted as the result of apatite weathering of the topsoil. Speciation modeling on soil extracts supported this idea: hydroxyapatite was not thermodynamically stable in the top 50 cm of the soil. Apatite was enriched in the bulk soil relative to the clay fraction, as expected during apatite dissolution. Combined results from batch experiments, XANES spectroscopy and X-ray diffraction suggested chemical transformations of the topsoil as a result from accumulation of organic matter and airing from tillage followed by enhanced weathering of apatite, amphiboles, clay minerals, and iron oxides. This caused the formation of poorly crystalline secondary iron and aluminum (hydr)oxides in the topsoil, which retained part of the released P from apatite. Other P was incorporated into organic forms. Furthermore, the results also showed that short-term acidification below the current pH value (below 5.5 in the topsoil and 7.2 in the deeper subsoil) caused significant solubilization of P. This is attributed to two different mechanisms: the instability of Al-containing sorbents (e.g. Al hydroxides) at low pH (in the topsoil), and the acid-mediated dissolution of apatite (the subsoil). (C) 2016 Elsevier B.V. All rights reserved.

Risk assessment for elevated leaching losses of phosphorus (P) from agricultural land is commonly based on indices, since such losses are highly episodic and difficult to predict. Here a flashiness index (FI) representing changes in daily water flow from drainage systems was estimated from measured discharge (agrohydrological years 2004–2013) after reconstruction of subsurface drainage systems in 16 fields on a former swine farm. The fields were analysed for ammonium lactate-extractable soil P (P-AL), clay, carbon and other soil parameters in 2004. Transport of total P (TP), dissolved reactive P (DRP) and unreactive P (UP) was estimated from concentrations in composite water samples taken flow-proportionally up to 20 times per year. On average, 2.20 kg TP ha−1 yr−1 was leached, with 27% in DRP form, from the entire farm. FI was significantly negatively correlated (Pearson correlation coefficient p < 0.05) to mean yearly discharge from each field. Stepwise regression demonstrated that FI index was the most important single explanatory parameter for flow-proportional yearly mean concentration of unreactive P losses (UP) from each field, with a coefficient of determination (r2) of 0.67. The corresponding concentration of dissolved reactive P (DRP) was significantly positively correlated (p = 0.015) to soil P-AL and FI. A regression model for TP leaching losses based on FI, P-AL and yearly discharge (Q) from 11 of the fields over nine years (r2 = 0.67, p = 0.002) was validated against TP leaching from the remaining five fields (32% of farm area). Root mean square error (RMSE) was 0.43, which represented 20% of measured leaching (mean 2.14 kg TP ha−1 yr−1). For individual years, RMSE for different fields was 37–80% of measured TP leaching (0.8–3.7 kg TP ha−1 yr−1). The FI index could be used together with soil P test to predict P leaching from individual fields of a drained farm.

Due to rapid growth of the horse industry in the EU, manure production from horse farms has become substantial. Horse manure is a valuable resource in terms of plant nutrients that should be utilised primarily as a fertiliser and soil conditioner on agricultural soils, but in an environmentally friendly manner. This study estimated potential retention and leaching losses of phosphorus (P), nitrogen (N) and carbon (C) from two mineral (Nantuna loamy sand and Wiad loam) and one organic (Hidinge peat) agricultural topsoil amended with two levels of composted horse manure, 18 and 36 megagram (Mg) ha − 1 , compared with non-amended control soil. Soil columns (20 cm long, 18.8 cm diameter) were exposed to three consecutive simulated rainfall events with an intensity of 8 mm h − 1 and a pore volume of 100 mm each time, which resulted in about 280 mm total discharge. Results showed that the background losses from Hidinge peat were several-fold higher (8 kg P, 122 kg N, 235 kg C ha − 1 ) than from Nantuna loamy sand (0.05 kg P, 2 kg N, 12 kg C ha − 1 ) or Wiad loam (1.6 kg P, 24 kg N, 19 kg C ha − 1 ). On applying composted horse manure the leachate concentrations of P, N and C significantly increased for the mineral soils, but only at the high application rate of 36 Mg ha − 1 . Unexpectedly, P, N and C concentrations in leachate from organic soil decreased after manure addition, indicating greater potential for retention than leaching. The increased amounts of P, N and C lost from Nantuna loamy sand and Wiad loam corresponded to less than 10% of the amount added via composted manure, indicating high potential for retention. We concluded that composted horse manure can improve soil nutrient status, as potential nutrient retention was higher than leaching from manure-amended soils, and that information on background nutrient content in soil may be more important than data on nutrient load applied through amendments when assessing retention and/or leaching potential in manure-amended soil.

Seven constructed wetlands (0.05–0.69 ha), situated in agricultural catchments (22–267 ha) in the south of Sweden, were studied for two years with two aims: to (i) quantify their function as sinks for particles and phosphorus (P) lost from the catchments, and (ii) investigate to what degree catchment and wetland characteristics and modeled loads (using hydrochemical catchment models) could be used to explain differences in retention between the wetlands. The wetland areas ranged from 0.04 to 0.8% of the respective catchment area, and they were situated in areas dominated by fine-textured soils with relatively high P losses and the main proportion of P transported in particulate form. Net P and particle retention were estimated during two years from annual accumulation of particles on sedimentation plates (40 × 40 cm) on the bottom of the wetlands. There was an annual net retention of particles and P, but with a large variation (for particles 13–108 t ha−1 yr−1 and for P 11–175 kg ha−1 yr−1), both between wetlands and between years. The difference between the two years was larger than the difference in mean P retention between the seven wetlands. There was a positive relationship between P and particle retention and three catchment factors, i.e. P status (P-AL) of agricultural soils, average slope in the catchments and the livestock density, and a negative relationship with the agricultural soil clay content. In addition, there was a positive relationship with the wetland length:width ratio. Contrary to expectations, neither the modeled hydraulic load nor P load was significantly correlated with the measured particle and P retention. There was also a positive relationship between P concentration in the sediment and soil P status in the catchment. The results imply that considerable errors are introduced when down-scaling modeled regional nutrient losses to estimate the P loads to small wetlands in agriculturally dominated catchments. A more qualitative approach, using catchment characteristics for identification of hot-spot fields, may be equally good to identify suitable locations for constructed wetlands to reduce diffuse P loads.

Leaching losses of nitrogen (N), phosphorus (P) and potassium (K) from arable land can be high, with N and P contributing significantly to the eutrophication of lakes and coastal waters. This study examined whether agriculture management and drain repair changed the chemical properties of shallow groundwater and affected nutrient leaching in the field. The hydrology of a subsurface-drained agricultural observation field included in the Swedish water quality monitoring programme was simulated for the period 1976–2006 using the process-based, field-scale model DRAINMOD. On the assumption that the drainage system operated similarly before and after repair, 54% more water was assigned to low-moderate flow events. Measured concentrations of sulphate-sulphur (SO4-S), sodium (Na), chloride (Cl) and potassium (K) were significantly lower in shallow groundwater in the period before drainage system repair (1980–1998) than afterwards (1998–2010). The concentrations were also significantly correlated with the corresp...

The importance of subsoil features for phosphorus (P) leaching is frequently mentioned, but subsoil effects are still poorly documented. This study examined whether the subsoil of four agricultural Swedish soils (two sand and two clay) functioned as a source or sink for P leaching by measuring P leaching from intact soil columns with topsoil (1.05 m deep) and without topsoil (0.77 m deep) over 3 yr. One sandy soil with high topsoil P content (Olsen P, 84 mg kg) and high subsoil sorption capacity (P sorption index [PSI], 3.7 mmol kg) had low leaching of dissolved reactive P (DRP) from full-length and subsoil lysimeters (0.12 and 0.08 kg ha yr, respectively). The other sandy soil, with high Olsen P content in the topsoil and subsoil (27 and 19 mg kg, respectively) and low PSI in the subsoil (1.4 mmol kg), had high DRP leaching from full-length and subsoil lysimeters (3.33 and 3.29 kg ha yr, respectively). High P content at depth (Olsen P, 21 mg kg) in one clay soil resulted in relatively higher subsoil DRP contribution (89%) to total leaching than observed in the other clay soil (71%). These results indicate that the subsoil can act as source or sink for P leaching, depending on P content, degree of P saturation, and P sorption capacity, and therefore subsoil properties should be considered when selecting mitigation measures to reduce P leaching.

Of the EU countries, Sweden utilizes the highest proportion (10%) of its total agricultural land for horses. Horse paddocks commonly hold horses on a limited space, in the present study at a rate of 5–14 livestock units ha−1. Thus these paddocks receive significant amounts of phosphorus (P) and nitrogen (N) through feed residues and deposition of feces and urine, which can lead to nutrient build-up in the soil. This study examined soil P and N status in different parts of horse paddocks (feeding, grazing and excretion areas) and compared it with that in adjacent, unmanaged reference soils. The paddock areas were then categorized with respect to environmental risk using the threshold concentrations of plant-available P extracted with ammonium acetate lactate solution at pH 3.75 (P-AL) and total N set by the Swedish Environmental Protection Agency. In total, seven horse farms, covering different grazing densities and soil textures representative of Swedish horse paddocks, were examined. The results showed that concentrations of water-soluble P (WSP), P-AL, and total N were highest in feeding and excretion areas within the paddocks. Weighted concentrations of soil P for the whole paddocks amounted to 2.9–10.5 mg WSP kg−1 and 35–224 mg P-AL kg−1, and were higher than in the corresponding reference fields (0.8–4.9 mg WSP kg−1 and 17–102 mg P-AL kg−1). The WSP concentration in the paddocks was strongly correlated with horse density (R2 = 0.80***1, n = 13) and P-AL with years of paddock management (R2 = 0.78***, n = 13). Total organic C was significantly correlated with P-AL, total P and total N in the feeding and excretion areas. The degree of soil P saturation percentage (DPS%) were important soil parameters determining WSP concentration in the paddocks (R2 = 0.63***, n = 110), whereas total P concentration in soils were determining P-AL concentrations (R2 = 0.82***, n = 112). According to Swedish environmental guidelines, two of the seven farms studied posed a high risk and three a moderate risk of extensive P leaching losses, but the risk of extensive N losses was moderate for all farms studied. As regards the specific sections of the paddock, the feeding and excretion areas had the highest risk of P leaching losses. Thus paddock soils can be high-risk areas for P leaching comprising about 3.85% of the total high-risk land area in Sweden.

Transport of phosphorus (P) from agricultural fields to water bodies deteriorates water quality and causes eutrophication. To reduce P losses and optimize P use efficiency by crops, better knowledge is needed of P turnover in soil and the efficiency of best management practices (BMPs). In this review, we examined these issues using results from 10 Swedish long-term soil fertility trials and various studies on subsurface losses of P. The fertility trials are more than 50 years old and consist of two cropping systems with farmyard manure and mineral fertilizer. One major finding was that replacement of P removed by crops with fertilizer P was not sufficient to maintain soil P concentrations, determined with acid ammonium lactate extraction. The BMPs for reducing P leaching losses reviewed here included catch crops, constructed wetlands, structure liming of clay soils, and various manure application strategies. None of the eight catch crops tested reduced P leaching significantly, whereas total P loads were reduced by 36% by wetland installation, by 39 to 55% by structure liming (tested at two sites), and by 50% by incorporation of pig slurry into a clay soil instead of surface application. Trend analysis of P monitoring data since the 1980s for a number of small Swedish catchments in which various BMPs have been implemented showed no clear pattern, and both upward and downward trends were observed. However, other factors, such as weather conditions and soil type, have profound effects on P losses, which can mask the effects of BMPs.

Lag times in reduced nutrient leaching after improved agricultural practices must be assessed to inform management decisions and evaluate their cost-effectiveness. This study estimated the leaching of phosphorus (P) and nitrogen (N) at two scales, a 33.8-ha nested field (data from 1973 to 2011) and an 820-ha agricultural catchment (data from 1992 to 2010). Field management was evaluated along with long-term nutrient trends. Estimates including and excluding nutrient concentrations in the stream under dry catchment conditions (mean 2.5 months year−1) revealed that wastewater contributed 10% of the total P (TP) catchment leaching, mostly in dissolved reactive (DRP) form. More recent flow-proportional sampling at the two scales demonstrated 45% higher particulate P leaching from the field than with discrete water sampling, whereas a past discrete sampling strategy may have overestimated DRP contributions to the stream. The accumulated field P balance was increasingly negative after 1987, whereas crop yields increased. From 1998, the measured accumulated TP leaching from the field was lower than the mean accumulated leaching, considering the estimated downward trend (−10%) over the 38-year study period (p

Catch crops are a potential option to reduce phosphorus (P) losses, but little is known about their establishment success and capacity to retain P on clayey soils in regions with short autumns, e.g. Sweden. This study screened biomass production and P retention by eight catch crop species: the perennials chicory (Cichorium intybus L), cocksfoot (Dactylis glomerata L), perennial ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L) and the annuals phacelia (Phacelia tanacetifolia L), white mustard (Sinapis alba L), oilseed radish (Raphanus sativus L oleiformis) and white radish (R. longipinnatus). The catch crops were grown at six field sites, where the perennial species were under-sown with barley and the annual species were after-sown following barley harvest. Biomass production, P content in above-ground and below-ground plant parts and content of available P in the soil were determined in autumn and survival rate of the catch crops in the following spring. Biomass production and P retention in autumn both differed significantly between species (p < 0.0001), and were greatly affected by site-specific conditions and time of sowing, which differed between experiments. Growth of catch crops can also be suppressed by low precipitation. Content of P in roots varied substantially between species, a factor which must be considered in species comparisons. The under-sown species produced more or equivalent amounts of biomass, retained more or equivalent amounts of P in autumn and survived better over winter than the after-sown species. Thus under-sown catch crops generally seem more suitable as catch crops for P.

High application rates of poultry ( Gallus gallus domesticus ) manure can impair drainage water quality through enhanced leaching of phosphorus (P) and nitrogen (N). In two years with application rates of broiler chicken manure corresponding to 99 and 79 kg P ha −1 year −1 to a tile-drained field with loamy soil in SW Sweden, mean concentrations of dissolved reactive P (DRP) were significantly higher ( p 3 -N) in peak, base and intermediate flows occurred in the 8-year period following manure application. Mean NO 3 -N concentration in peak flows decreased approximately linearly, by 5.6 μg L −1 , for every mm of total water discharge. Thus poultry manure should not be applied in repeated high loads in order to avoid the risk of enhanced P leaching losses during subsequent peak flows. Furthermore, N leaching losses during peak and base flow conditions can persist for longer than a 5-year crop rotation and were shown here to recede at a slower relative rate than P.

Assessing mitigation of phosphorus (P) leaching from subsurface drainage systems is challenging due to high spatial and temporal variation in leaching. Mean measured total P leaching from a clayey soil in an eight-year study period (four replicates per treatment) was (kg ha-1 year-1): 1.21 from shallow autumn tillage (ShT), 0.84 from unfertilised fallow (UF), 0.81 from conventional autumn ploughing (CT) and 0.57 from structure liming (SL-CT). Treatment was not significant using Richards-Baker flow index or a distance factor as covariate (p = 0.084 and 0.057). A tendency for lower leaching was obtained comparing SL-CT with ShT (p adjusted = 0.060 and 0.009 respectively). A combination of measures adapted to drainage conditions and clay content in different parts of the field is proposed since P leaching was approximately halved from an adjacent field (4.3 ha) in a three-year post-period compared with a three-year pre-period for structure liming the entire field and drainage system renovation plus structure lime drain backfilling.

It is suggested that catch crops be grown to reduce phosphorus (P) losses. However, after exposure to freezing–thawing cycles (FTCs), catch crop material can become a source of P losses to waters in moderately cold climates. This study screened potential P leaching from intact plant material of eight catch crop species: chicory (Cichorium intybus L.), cocksfoot (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), red clover (Trifolium pratense L.), phacelia (Phacelia tanacetifolia L.), white mustard (Sinapis alba L.), oilseed radish (Raphanus sativus L. oleiformis) and white radish (R. longipinnatus). The catch crops were grown in six field experiments on clay soils, where soil lysimeters (0.25 m deep) with intact crops were extracted in autumn and used for leaching experiments before and after seven FTCs in the laboratory. The eight catch crops did not reduce P leaching before FTCs. After FTCs, leachate total-P concentrations from ryegrass, oilseed radish and red clover lysimeters were significantly (p = 0.0022) higher than those from the other species and the control without a catch crop. FTCs significantly (p = 0.0064) altered total-P concentration and the proportions of different forms of P. There was a significant increase in total-P concentration in leachate from ryegrass (p = 0.0008) and oilseed radish (p = 0.02). Thus the potential risk of P leaching from ryegrass and oilseed radish material after FTCs must be considered, since they are commonly grown as nitrogen catch crops in the Nordic countries. Moreover, the roots of the tested catch crops contained 7–86 % total-P, which is important when evaluating P leaching risks.

The EU Water Framework Directive (WFD) obliges Member States to improve the quality of surface water and groundwater. The measures implemented to date have reduced the contribution of point sources of pollution, and hence diffuse pollution from agriculture has become more important. In many catchments the water quality remains poor. COST Action 869 was an EU initiative to improve surface water quality that ran from 2006 to 2011, in which 30 countries participated. Its main aim was a scientific evaluation of the suitability and cost-effectiveness of options for reducing nutrient loss from rural areas to surface waters at catchment scale, including the feasibility of the options under different climatic and geographical conditions. This paper gives an overview of various categories of mitigation options in relation to phosphorus (P). The individual measures are described in terms of their mode of action, applicability, effectiveness, time frame, environmental side-effects (N cycling) and cost. In total, 83 measures were evaluated in COST Action 869.

Constructed free water surface wetlands (CWs) are used to reduce nutrient and sediment loads to receiving waters in highly impacted catchments by e.g., agricultural land use. In this paper, we evaluated the retention effectiveness of a Swedish CW in two consecutive hydrological years, 3-4 years after construction respectively. We compared nutrient loads based on concentrations from flow-proportional sampling (C-fp) and turbidity and nitrate concentrations measured with optical sensors (C-s). CW's retention was estimated based on differences between inlet and outlet concentrations and flow (Q) at both the inlet and outlet (2Q), or only at the inlet (1Q). In the first year (2012/2013), with a cold winter (mean topsoil temperature -0.2 degrees C), nitrate-nitrogen (NO3N) retention was 32% (C-fp and C-s, 2Q). In the second year, with a mild winter (mean topsoil temp 1.8 degrees C) and less water runoff, the corresponding values were 37% (C-fp, 2Q) and 39% (C-s, 2Q). Nitrate-nitrogen retention was significantly correlated to water residence time and temperature, and was most effective relative to the load (80%) in summer and least effective (40%) in winter. Quantitatively, however, summer NO3N retention contributed only 7% (2Q) or 8% (1Q) of yearly NO3N mass retention. Particulate phosphorus (PP) concentrations were significantly correlated with suspended solids (SS) concentrations at both inlet and outlet. Seasonal PP retention (C-fp, 2Q) was related to particle residence time estimated from turbidity measurements by sensors, and was less effective in the cold winter (3%) than in the mild winter (32%) (C-fp, 2Q). Yearly retention (2Q) as a mean of the two years was: SS 40%, total P 36%, PP 34%, dissolved reactive P 30%, total N 56%, NO3N 35%, organic N 75%, and organic C 30%. Overall, the wetland satisfactorily removed nutrients from agricultural drainage water. However, longer-term studies over a range of flow and temperature conditions are needed to evaluate climate conditions and hydrological residence time as key factors in nutrient removal efficiency.

Of the EU countries, Sweden utilizes the highest proportion (10%) of its total agricultural land for horses. Horse paddocks commonly hold horses on a limited space, in the present study at a rate of 5–14 livestock units ha−1. Thus these paddocks receive significant amounts of phosphorus (P) and nitrogen (N) through feed residues and deposition of faeces and urine, which can lead to nutrient build-up in the soil. This study examined soil P and N status in different parts of horse paddocks (feeding, grazing and excretion areas) and compared it with that in adjacent, unmanaged reference soils. The paddock areas were then categorized with respect to environmental risk using the threshold concentrations of plant-available P extracted with ammonium acetate lactate solution at pH 3.75 (P-AL) and total N set by the Swedish Environmental Protection Agency. In total, seven horse farms, covering different grazing densities and soil textures representative of Swedish horse paddocks, were examined. The results showed that concentrations of water-soluble P (WSP), P-AL, and total N were highest in feeding and excretion areas within the paddocks. Weighted concentrations of soil P for the whole paddocks amounted to 2.9–10.5 mg WSP (kg−1) and 35–224 mg P-AL (kg−1), and were higher than in the corresponding reference fields (0.8–4.9 mg WSP (kg−1) and 17–102 mg P-AL (kg−1)). The WSP concentration in the paddocks was strongly correlated with horse density (R2 = 0.80*** 1 , n = 13) and P-AL with years of paddock management (R2 = 0.78***, n = 13). Total organic C was significantly correlated with P-AL, total P and total N in the feeding and excretion areas. The degree of soil P saturation (DPS) concentrations was important soil parameters determining WSP concentration in the paddocks (R2 = 0.63***, n = 110), whereas total P concentration in soils was determining P-AL concentrations (R2 = 0.82***, n = 112). According to Swedish environmental guidelines, two of the seven farms studied posed a high risk and three a moderate risk of extensive P leaching losses, but the risk of extensive N losses was moderate for all farms studied. As regards the specific sections of the paddock, the feeding and excretion areas had the highest risk of P leaching losses. Thus paddock soils can be high-risk areas for P leaching comprising about 3.85% of the total high-risk land area in Sweden.

Overall, arable soils in Sweden are currently generally close to phosphorus (P) balance, but excessive P accumulation has occurred on animal fur farms, i.e., those rearing mink (Mustela vison) and foxes (Alopex lagopus and Vulpes vulpes). Manure P from these farms has sometimes regarded as sparingly soluble. Laboratory lysimeter topsoil trials with simulated rain demonstrated that potential leaching of P in dissolved reactive form (DRP) can be very high, even for heavy clay (50%–65%) soils. The Swedish/Norwegian soil test P-AL (soil P extracted with acid NH4 lactate, AL) proved useful as a potential indicator of DRP leaching risk (regression coefficient [R 2] = 0.89) from fur farms. The upper 5-cm soil layer, with 190% higher (median) soil P status than the 5–20 cm layer, was the major source of potential DRP leaching through soil columns at the site, despite having been under grass or green fallow for the past 8 y. In percolate from topsoil lysimeters, DRP concentration increased by 0.29 mg L–1 after the long-term manure application but only by 0.14 mg L–1 after the single slurry application when compared to no addition of slurry. Therefore, the build-up to a high soil P status due to the long-term application of mink manure was more important than a single application of pig slurry at a rate corresponding to 22 kg P ha–1 with respect to soil leachate DRP losses in this lysimeter study. The study stresses the importance of precision farming, in which the amount of slurry-P applied is based on testing the already existing soil P content.

Eutrophication, a major problem in many fresh and brackish waters, is largely caused by nonpoint-source pollution by P from agricultural soils. This lysimeter study examined the influence of P content, physical properties, and sorption characteristics in topsoil and subsoil on P leaching measured during 21 mo in 1-m-long, undisturbed soil columns of two clay and two sandy soils. Total P losses during the period varied between 0.65 and 7.40 kg ha. Dissolved reactive P was the dominant form in leachate from the sandy soils and one clay soil, varying from 48 to 76%. Particulate P dominated in leachate from the other clay soil, where low pH (5.2) in the subsoil decreased aggregate stability and thereby probably increased the dispersion of clay particles. Phosphorus leaching was small from soils with high P sorption index (PSI) and low P saturation (10% of PSI) in the subsoil, even though extractable P (Olsen P) in the topsoil was high, and large from a soil with low sorption capacity and high P saturation (35% of PSI) in the profile. High sorption capacity in the subsoil was more important for P leaching in sandy soils than in clay soils with macropore flow, where the effect of high sorption capacity was reduced due to less interaction between percolating water and the soil matrix. The results suggest that P leaching is greatly affected by subsoil properties and that topsoil studies, which dominate current research, are insufficient for assessing P leaching in many soils.

One measure used in Sweden to mitigate eutrophication of waters is the construction of small wetlands (free water surface wetland for phosphorus retention [P wetlands]) to trap particulate phosphorus (PP) transported in ditches and streams. This study evaluated P retention dynamics in a newly constructed P wetland serving a 26-ha agricultural catchment with clay soil. Flow-proportional composite water samples were collected at the wetland inlet and outlet over 2 yr (2010-2011) and analyzed for total P (TP), dissolved P (DP), particulate P (PP), and total suspended solids (TSS). Both winters had unusually long periods of snow accumulation, and additional time-proportional water samples were frequently collected during snowmelt. Inflow TP and DP concentrations varied greatly (0.02-1.09 mg L) during the sampling period. During snowmelt in 2010, there was a daily oscillation in P concentration and water flow in line with air temperature variations. Outflow P concentrations were generally lower than inflow concentrations, with net P losses observed only in August and December 2010. On an annual basis, the wetland acted as a net P sink, with mean specific retention of 69 kg TP, 17 kg DP, and 30 t TSS ha yr, corresponding to a reduction in losses of 0.22 kg TP ha yr from the agricultural catchment. Relative retention was high (36% TP, 9% DP, and 36% TSS), indicating that small constructed wetlands (0.3% of catchment area) can substantially reduce P loads from agricultural clay soils with moderately undulating topography.

In this study we investigated the phosphorus (P) content of Baltic soils. In the first set of analyses, 99 soil samples from the Baltic states and Sweden (soil set 1, representing seven different catchments or experimental plots) were analysed for soil P using four extraction methods: ammonium lactate (PAL), double lactate (PDL), Mehlich 3 (PM3) and carbonate (POlsen) (r = 0.85–0.97). In absolute values, results from PM3, PDL and POlsen gave means of 71, 61 and 20%, respectively, of the value from the PAL extraction method. Significantly different relationships were found between P soil concentrations and pH of the extract. In addition, soil pH and organic matter content were found to be of importance. Secondly, we tested 110 soil samples (soil set 2) from five different Swedish monitoring fields with clay soils where PAL clearly correlated with soil P extracted in calcium chloride (PCaCl2) (r = 0.95). Values of a single-point phosphorus sorption index (PSI) correlated with the aluminium concentration (AlAL) in the lactate extract (r = 0.91) and with (AlOX) in the oxalate extract (r = 0.96). None of the soil P tests with different extraction agents – calcium chloride (PCaCl2), water (Pw), POlsen or PAL– correlated with the mean annual flow-weighted concentration (1999–2010) of dissolved reactive P (DRP) in drainage water. Neither was there any clear relationship between DRP concentration in drainage water and these tests combined with PSI or with other sorption indices including extracted Al and iron (Fe). However, DRP was related to the clay content of the topsoil (r = 0.91, P

This review summarizes current knowledge from the literature and experimental studies on the role of cover crops (CCs) in reducing nitrogen (N) leaching and phosphorus (P) losses to waters under the marine and humid continental climate conditions of southern Scandinavia and Finland. Field leaching studies from 11 sites indicate that undersown ryegrass (Lolium spp.) CCs are robust, with average N uptake in aboveground CC biomass of 7 to 38 kg N ha−1 (6.2 to 34 lb N ac−1). Use of CCs sown at harvest (e.g., crucifers) is restricted to southern Scandinavia for climate reasons. The mean relative reduction in N leaching reported for all CCs investigated was 43%, but it ranged between 62% increase instead of a reduction after a red clover (Trifolium pratense) CC on a clay soil to a reduction of 85% to 89% with a perennial ryegrass CC on sandy soils in Denmark (36 to 51 kg ha−1 [32 to 46 lb ac−1]). The data indicate that CCs do not substantially reduce total P losses by runoff and leaching. The effects of CCs on total P leaching varied between a relative increase of 86% and a decrease of 43%. Climate conditions involving freezing-thawing during winter increased the risk of losses of dissolved P from CC biomass. CCs have been implemented to varying degrees into agri-environmental programs. They are mandatory in Denmark and subsidized in Norway, Sweden, and Finland. CCs are grown on 8% of arable land in Denmark, 5% in Sweden, 1% in Finland, and 0.5% in Norway, but CC area is now increasing dramatically in Finland due to a new subsidy program. In all countries there is a need, and potential, for increased use of CCs, but there are several constraints, particularly reduced interest among farmers. There is a clear need to identify CC systems and develop implementation strategies for appropriate distribution of CCs on different soils and regions with respect to required reductions in N leaching and P losses. For this, more knowledge is required, especially about the effect of CCs on P losses (e.g., the effect of species with different partitioning between shoot and root biomass and the effects of CC systems with harvesting of biomass). There is also a need to devise balanced solutions for maintaining and increasing the frequency of CCs in crop rotations to exploit the possible benefits of CCs in reducing nutrient losses.

Losses of commonly used chemical pesticides from agricultural land may cause serious problems in recipient waters in a similar way to phosphorus (P). Due to analytical challenges concerning determination of glyphosate (Gly), transport behaviour of this widely used herbicide is still not well-known. The objective of the present study was to quantify and evaluate leaching of Gly in parallel with P. Leaching losses of autumn-applied Gly (1.06 kg ha-1) via drainage water were examined by flow-proportional sampling of discharge from 20 drained plots in a field experiment in eastern Sweden. Samples were analysed for Gly in particulate-bound (PGly) and dissolved (DGly) form. The first 10 mm water discharge contained no detectable Gly, but the following 70 mm had total Gly (TotGly) concentrations of up to 6 µg L-1, with 62% occurring as PGly. On average, 0.7 g TotGly ha-1 was leached from conventionally ploughed plots, compared with 1.7 g TotGly ha-1 from shallow-tilled plots (cultivator to 12 cm working depth). Higher Gly losses occurred in snowmelt periods in spring, but then with the majority (60%) as DGly. All autumn concentrations of PGly in drainage water were significantly correlated (p

In 1988–2009, efforts involving manure regulations, subsidies and advisory work were made to reduce losses of nitrogen (N) and phosphorus (P) from arable land to water in Sweden, especially southern Sweden. To evaluate ensuing long-term trends, nutrients in total and dissolved form were monitored in drainage water from 13 fields under ordinary cultivation. The Mann-Kendall test, adjusted for biweekly sampling, revealed significant decreasing trends (magnitude 3% per year) in nitrate–nitrogen (NO 3 –N) concentrations in two fields. One of these had received no manure and had been subjected to delayed tillage after fallow since 1993, while the other had been frequently cropped with a catch crop combined with spring tillage since 1999. An additional decreasing trend in dissolved reactive P (DRP) was observed over the years from this and another field, both with unfertilised fallow grown as an interior buffer on an area at the field outlet, one in 1999–2010 and the other since 2001. By contrast, there was an increasing trend in DRP in a field with accelerating P loads that included almost yearly manure additions to crops following potatoes and sugar beet. However, the general DRP level in the drainage water was low (4–13 μg L −1 ), probably as a result of high P sorption capacity of the topsoil and subsoil. No significant trends in total P or particulate P were found for any of the fields. The importance of long-term monitoring of nutrients in water leaving agricultural fields in order to estimate trends in nutrient losses is discussed.

Summary A refined version of a conditional phosphorus risk index (PRI) for P losses to waters was developed based on monitoring and analyses of PRI factors from an agricultural catchment in Sweden. The catchment has a hummocky landscape of heavy glacial till overlying moraine and an overall balanced soil P level. Single P source factors and combinations of factors were tested and discussed together with water movement and water management factors important for catchments dominated by drained clay soils. An empirical relationship was established (Pearson correlation coefficient 0.861, p 2 ), measured in a weak calcium chloride solution, and iron (Fe-AL) aluminium (Al-AL) and phosphorus (P-AL) in soil extract with acid ammonium lactate. Differing relationships were found for a field that had not received any manure in the last 15 years and a field that had received chicken litter very recently. In addition, a general relationship (Pearson correlation coefficient 0.839, p 2 and the degree of phosphorus saturation in lactate extract (DPS-AL). One exception was a single field, representing 7% of agricultural land in the catchment, that had been treated with glyphosate shortly before soil sampling. Saturated hydraulic conductivity (SHC) in heavy clay in contact with the moraine base (at 1 m depth) was on average 0.06 m day −1 . In clay not in contact with moraine, SHC was significantly lower (mean 0.007 m day −1 ). A reduction in the present tile drain spacing (from 14–16 m to 11 m) is theoretically required to maintain satisfactory water discharge and groundwater level. Up to 10% of the arable land was estimated to be a potential source area for P, based on different indices. Parts of a few fields close to farm buildings (1% of total arable land) were identified as essential P source areas, with high DPS-AL values and low PSI-CaCl 2 values throughout the soil profile. A further 2% of arable land was identified as potential important transport areas, based on visible surface water rills or frequent water-ponded conditions. Fields comprising 10% of the total arable land in the catchment should be re-drained in the near future to improve water infiltration and avoid unnecessary channelised water flow. The need for an improved PRI for erosion and water transport is discussed.

During 2005-2007, studies were carried out in two field experiments in southwest Sweden with separately tile-drained plots on a sandy soil (three replicates) and on a clay soil (two replicates). The overall aim was to determine the effects of different cropping systems with catch crops on losses of N, P and glyphosate. Different times of glyphosate treatment of undersown ryegrass catch crops were examined in combination with soil tillage in November or spring. Drainage water was sampled continuously in proportion to water flow and analysed for N, P and glyphosate. Catch crops were sampled in late autumn and spring and soil was analysed for mineral N content. The yields of following cereal crops were determined. The importance of keeping the catch crop growing as long as possible in the autumn is demonstrated to decrease the risk of N leaching. During a year with high drainage on the sandy soil, annual N leaching was 26 kg/ha higher for plots with a catch crop killed with glyphosate in late September than for plots with a catch crop, while the difference was very small during 1 yr with less drainage. Having the catch crop in place during October was the most important factor, whereas the time of incorporation of a dead catch crop did not influence N leaching from either of the two soils. However, incorporation of a growing catch crop in spring resulted in decreased crop yields, especially on the clay soil. Soil type affected glyphosate leaching to a larger extent than the experimental treatments. Glyphosate was not leached from the sand at all, while it was found at average concentrations of 0.25 μg/L in drainage water from the clay soil on all sampling occasions. Phosphorus leaching also varied (on average 0.2 and 0.5 kg/ha/yr from the sand and clay, respectively), but was not significantly affected by the different catch crop treatments.

Concentrations of dissolved reactive phosphorus (C DRP ) and particle-bound phosphorus (C PP ) were investigated in soil columns taken from different parts of three selected agricultural fields. The columns (mini-lysimeters 20 cm in diameter, 20 cm high) were exposed to on average 64 ± 6 mm of simulated rainfall. Total phosphorus concentrations (C TP ) in water percolating from the lysimeters were similar to the C TP observed in drainage water leaving the fields, but the C DRP /C TP ratio was significantly ( p DRP (up to 0.4 mg L − 1 ) measured in the percolate may have partly derived from decomposition of accumulated senescing vegetation and litter material, since C DRP in percolating water was related to total organic carbon concentration (TOC) in the shallow topsoil (0–5 cm) and to phosphorus concentration in soil extract of ammonium lactate (P-AL) from the same soil layer. Another easily identified factor clearly related to C DRP in percolate from the lysimeters was the degree of phosphorus saturation (DPS) in the same soil P-AL extract. The factors giving best prediction of C PP and leaching were the amount of percolate passing through the soil columns and total phosphorus concentration in the topsoil determined after oxidation with nitric acid (TP-HNO 3 ). One field under grass ley, including the slope and depression close to the field outlet, comprised 24% of total field area. In the other two fields these areas (11 and 17% of total area respectively) were under long-term permanent green fallow as an internal buffer zone (IBZ). The lysimeter studies indicated that these areas had a higher risk of DRP losses than the rest of the fields. In addition, the P content of the particles in water from the depression was unusually high. Aggregate stability, measured indirectly as readily dispersible clay and expressed as nephelometric turbidity units (NTU), was significantly stronger at the lowest point of one IBZ (27–35 NTU) than in stubbled parts of the same field (62 NTU), and the turbidity of water percolating through the topsoil was lower (5–27 NTU).

In Scandinavia high losses of soil and particulate-bound phosphorus (PP) have been shown to occur from tine-cultivated and mouldboard-ploughed soils in clay soil areas, especially in relatively warm, wet winters. The omission in the autumn of primary tillage (not ploughing) and the maintenance of a continuous crop cover are generally used to control soil erosion. In Norway, ploughing and shallow cultivation of sloping fields in spring instead of ploughing in autumn have been shown to reduce particle transport by up to 89% on highly erodible soils. Particle erosion from clay soils can be reduced by 79% by direct drilling in spring compared with autumn ploughing. Field experiments in Scandinavia with ploughless tillage of clay loams and clay soils compared to conventional autumn ploughing usually show reductions in total P losses of 10–80% by both surface and subsurface runoff (lateral movements to drains). However, the effects of not ploughing during the autumn on losses of dissolved reactive P (DRP) are frequently negative, since the DRP losses without ploughing compared to conventional ploughing have increased up to fourfold in field experiments. In addition, a comprehensive Norwegian field experiment at a site with high erosion risk has shown that the proportion of DRP compared to total P was twice as high in runoff water after direct drilling compared to ploughing. Therefore, erosion control measures should be further evaluated for fields with an erosion risk since reduction in PP losses may be low and DRP losses still high. Ploughless tillage systems have potential side-effects, including an increased need for pesticides to control weeds [e.g. Elytrigia repens (L.) Desv. ex Nevski] and plant diseases (e.g. Fusarium spp.) harboured by crop residues on the soil surface. Overall, soil tillage systems should be appraised for their positive and negative environmental effects before they are widely used for all types of soil, management practice, climate and landscape.

Leaching of nutrients was studied at a tile drain outlet and in two pairs of groundwater pipes in an arable field in central Sweden in order to identify trends and impacts of the climate. In the study period (1973–2005), crop production was dominated by spring barley, winter wheat, rape and, in later years, potatoes. Winter crops were cultivated 60% of the time. Leaching of total nitrogen (TotN) and total phosphorus (TotP) to drain water was low, on average 10 kg ha−1 year−1 for TotN and 0.07 kg ha−1 year−1 for TotP based on measurements. Nitrogen fertilisation increased slightly from 121 to 142 kg ha−1 year−1 during the period in a balanced way in line with increasing crop yields of cereals, from 5.8 to 6.6 tonnes year−1. For the entire study period, the temperature was estimated to increase significantly by a total of +2 °C for the growing season (April–September). Precipitation (+16 mm) and humidity (+11%) were also estimated to have increased significantly, mainly in June. Simulations with a ...

Leaching of nutrients and major ions from a tile-drained arable field was evaluated over a 25-year period (1980–2005). The soil, classified as a Gleyic Cambisol, received moderate applications of fertilizers. During later years the soil was more frequently under ley, and since 2002, an area of ravine (29% of the total field) has been managed as a permanent fallow with annual cutting without removing the grass material. A decrease in the concentration of nitrate nitrogen (NO3−N) in the drainwater was estimated in 1980–2005, based on non-parametric tests on concentrations flow-normalized with a robust fitting curve procedure. The average concentration of soluble reactive phosphorus after pre-filtration (RPf) of 0.030 mg l−l corresponded to a calculated degree of phosphorus saturation (DPS) of 6% in acid extract of ammonium lactate from the topsoil. Between 1995 and 2005, concentrations of suspended solids (SS), RP and total organic carbon (TOC) decreased significantly in the drainage water from the...

The aim of this study was to evaluate the long-term (1977–2004) effects of new agricultural practices and reduced acid rain on drainwater and groundwater chemistry for an intensely cultivated arable field with sandy soil in south-west Sweden. Trends in chemical composition of the drainwater were compared with those of atmospheric deposition and groundwater. A modified crop rotation including catch crops significantly decreased the average concentration of nitrate nitrogen (NO3-N) in drainwater from 13.0 to 7.2 mg L−l. This rotation was also found to be a very effective measure against high NO3-N concentrations in shallow groundwater (1.7 m below the soil surface). The degree of phosphorus saturation (DPS) in the subsoil, calculated to be 10% and 9% by two different laboratory methods, corresponded to an average and constant concentration of dissolved reactive phosphate (DRP) in drainwater of 0.006 mg l−l. Generally lower inputs of acid deposition to the soil were confirmed by a decreasing SO4-S trend (by 3% over 24 years) in drainwater. Changes in cropping had reduced the acid load to the soil, while drainwater alkalinity showed a slow but significant positive trend amounting to 0.4% over 24 years.

Adapting regional eutrophication targets for surface waters - influence of the EU water framework directive national policy and climate change

In the north-western European countries Norway, Sweden, United Kingdom (UK) and Ireland, variability in the forms, amounts and timing of phosphorus (P) loss from agricultural land is related to national differences in climate, soil, hydrological conditions and agricultural production. The dissolved form of P constitutes 9–93% of the total phosphorus (TP) in water, subsurface drainage can contribute 12–60% and surface erosion 40–88% of TP transfer. TP export in small agricultural streams is generally in the range 0.3–6 kg/ha/year, with the highest losses in Norway and UK. All four countries are complying with the EU Water Framework Directive and developing a range of measures based on P source with transport controls over P losses. A decreasing trend in TP losses has been detected in agricultural streams following the introduction of measures to reduce erosion in Norway. Average P concentrations in Swedish streams have shown a reduction of nearly 2% per year since 1993 as a result of measures introduced in southern Sweden. However, in two large rivers in agricultural regions of Sweden, the concentrations of suspended solids (SS) and TP were shown to increase by 0.4% and 0.7% per year, respectively, over the period 1975–2004, possibly as a result of climate change. It is too early to detect trends in agricultural contributions to P in surface waters as a result of catchment-sensitive farming (CSF) in the UK and Ireland.

Diffuse phosphorus losses from arable land contribute significantly to eutrophication in many regions. To enable the most efficient measures for reducing P losses to be identified, it is important to quantify the contributions from different sources and the effects of various scenarios aimed at reducing these losses. To account for transport to tile-drains through macropores, we extended the field-scale simulation model ICECREAM with descriptions based on mixing layer and dual porosity concepts. For losses of particulate phosphorus (PP) to tile-drains, a new description of particle generation and detachment was included. The model was applied on a 6-year field experiment on a structured clay soil in south-west Sweden and simulation results were compared with measured water flow and losses of suspended particles (SP), PP and dissolved reactive phosphorus (DRP) to tile-drains. After calibration of parameters related to macropore flow and transport, and to particle generation and detachment, the model could describe the extremely episodic losses of SP, PP and DRP reasonably accurately. However, some short-term fluctuations were not captured (model efficiency during the validation period −2.1 for PP and 0.43 for DRP). Thus, further development and testing are required before the model can be used with confidence for predictive applications or management purposes. Based on this application, we suggest that direct leaching from non-decomposed plant material and infiltration in partly frozen soil be included in the ICECREAM model. We also suggest that the controls on the sorption distribution coefficient for partitioning between DRP and labile phosphorus (PL) and the effects of using the ‘storage routing’ equation for calculation of soil water content instead of the Richards equation be further investigated.

Phosphorus (P) binding to minerals and ion exchange capacity in different clay fractions were examined for a non-calcareous soil in southwest Sweden. The soil had received pig slurry during three decades, 2 kg lower than the recent maximum load of 22 kg P ha − 1 year − 1 as regulated by livestock density legislation. The topsoil was found to contain 33% clay by weight. Illite was the predominant clay mineral and constituted 13% of total soil. Vermiculite (10%), K-feldspar (14%) and plagioclase (21%) also constituted significant proportions of the mineralogical matrix. Within the most fine-grained clay fraction, 50% of which was less than 0.1 μm in particle size, illite and vermiculite dominated totally, 50 and 23% respectively. In fine-grained (FG), most fine-grained (MFG) and colloidal fractions, there were strong relationships (Pearson correlation coefficient 0.98–1.00) between calcium (Ca) and P. There was a low molar ratio Ca:P in added manure and the presence of Ca–P complexes in the fine soil fractions was indicated. In contrast, in the coarse soil fraction (> 2 μm), there was a clear relationship (Pearson coefficient 0.97) between P and iron oxide (Fe 2 O 3 ) and between P and aluminium oxide (Al 2 O 3 ) throughout the soil profile. Thus even for non-calcareous soils, formation of Ca–P complexes should be taken into account with regards to losses of colloidal P to drainage water.

The series of papers in this issue of AMBIO represent technical presentations made at the 7th International Phosphorus Workshop (IPW7), held in September, 2013 in Uppsala, Sweden. At that meeting, the 150 delegates were involved in round table discussions on major, predetermined themes facing the management of agricultural phosphorus (P) for optimum production goals with minimal water quality impairment. The six themes were (1) P management in a changing world; (2) transport pathways of P from soil to water; (3) monitoring, modeling, and communication; (4) importance of manure and agricultural production systems for P management; (5) identification of appropriate mitigation measures for reduction of P loss; and (6) implementation of mitigation strategies to reduce P loss. This paper details the major challenges and research needs that were identified for each theme and identifies a future roadmap for catchment management that cost-effectively minimizes P loss from agricultural activities.

Keeping beef cattle outdoors during winter reduces costs and improves animal welfare, but in- creases the risk of nitrogen (N) and phosphorus (P) runoff losses. This study evaluated a rota- tional pen design on grassland with two groups of suckler cows given access to an expanding staying area and a new feeding area each week (72 cattle ha −1 ), with one month's stay per pen. The spatial distribution of excreta and effects on N and P surface runoff was evaluated during six months. The total excreta loads corresponded to 500 kg·N·ha−1 and 50 kg·P·ha−1. New feeding ar- eas did not distribute excretions evenly, which resulted in the highest proportion of excretions (31%) occurring in the first week's sub-area. The topsoil had significantly higher amounts of min- eral-N, mainly as NH4-N (29 - 81 kg·ha−1), than an unaffected area (13 kg·ha−1). Mean total runoff losses were similar for both groups (1.4 kg·P·ha−1 and 9.0 kg·N·ha−1). Around 78% of N and 70% of P runoff losses occurred during the month with cattle present. During the first two weeks with heavy rain, N and P runoff losses were 50% higher from an area with suckler cows than a corre- sponding vegetated sub-area without cows. The study design did not provide a sufficient distribu- tion of excretions and a high animal density in combination with trampling resulted in unaccept- able N and P run-off losses. An environmentally friendly design would need to include frequent moving of all equipment and access to larger areas.

Soil tests with extractions are commonly used for risk assessments of phosphorus (P) leaching. Procedures for routine analysis of crop-available soil P by extraction with acid ammonium lactate (P-AL) have been used for nearly 50 years in Sweden, Norway and several East European countries. Aluminium and iron (Al-AL and Fe-AL) were determined in the same extract for 40 well known clayey, loamy or sandy soils from the Swedish long-term studies. Average outcome was 16.8 and 6.0% for the two elements related to extraction with chelating ammonium oxalate (Al-AO and Fe-AO) and concentrations had a correlation coefficient of 0.947 and 0.891, respectively, when the two extraction agents were compared. On average, P-AL determination using inductive coupled plasma (ICP) resulted in 19% higher soil P concentrations compared to analysis using a colorimetric method based on non-calcareous and calcareous soils from the southern counties in the Swedish soil survey, represented mainly by sandy loam soils. Degree ...

Within the Swedish Monitoring Programme for Agriculture, 27 small agricultural catchments were investigated for between 9 and 14 years (6 years for one catchment), starting in the late 1980s, to determine the impact of agricultural activities on discharge water. The catchments represent major variations in climate, soil types and farming in Sweden and hence long-term average load of total nitrogen (N) and total phosphorus (P) at stream outlets varied widely among the catchments, from 2 to 41 and from 0.1 to 0.9 kg ha −1 yr −1 , respectively. Catchments with large N loads were characterised by several factors favourable for leaching, such as mild winter climate, large precipitation, sandy or organic soils and high animal density in combination with intensive cropping systems with a low percentage of ley. Large P loads were mainly related to factors such as clay and clay loam soils, medium to high precipitation and large proportions of annual crops in the catchments. Flow-normalised time series of monthly loads of nitrate N, phosphate P and particulate P (for 24 catchments) were tested for trends. Significant downward trends were revealed for nitrate N, phosphate P and particulate P for seven, eight and three catchments, respectively, whereas, upward trends were revealed for nitrate N and particulate P for one and two catchments, respectively. Downward nitrate N trends for two catchments were correlated to smaller amounts of applied manure, especially during autumn, and to a decrease in the area of spring cereals and spring rape.

Preferential flow may enhance phosphorus transport through the soil profile and thereby increase the risks for eutrophication of watercourses. Destruction of continuous macropores in topsoil by tillage provides the possibility for better contact between soil particles and P fertilizer. This is facilitated by incorporation rather than surface application of fertilizer, which should reduce the risk of rapid P transport from the soil surface through the unsaturated zone. To test this hypothesis, undisturbed soil monoliths (0.295m in diameter and 1.2 m in length) were collected at a field site with a clay soil in which preferential flow is the dominant solute transport mechanism. After three years of observation, average total P loads reached 1.86, 1.59 and 1.25 kg ha -1 for no-tillage, conventional tillage, and conventional tillage where the P fertilizer was incorporated, respectively. More than 80% of total losses were in the form of dissolved P. The tillage treatment had no significant effect on P leaching loads compared to no-tillage, but the improved contact between soil particles and P fertilizer resulting from fertilizer incorporation significantly reduced P loads during the first year after application of 100 kg P ha -1 . However, after further application of 100 kg P ha -1 two years later, there were no significant differences between the treatments.

A long-term lysimeter experiment with undisturbed monoliths studied leaching behaviour and balances of phosphorus (P), potassium (K) and nitrogen (N) during a seven year crop rotation on four types of soil receiving inorganic fertilizers, manure and grass compost respectively It was shown that application of manure did not lead to any direct change in nutrient leaching, unlike the application of fertilizers to soils of normal fertility. However, soil type considerably affected the nutrient concentrations in the drainage water. Manure applied in amounts equal to the maximum animal density allowed by Swedish legislation slightly over-supplied P and N (0.5-3.5 and 18-38 kg ha -1 y -1 respectively) compared to the crop requirement and leaching losses for most of the soils. The relationship between lactate-soluble P in the topsoil and the concentrations of dissolved P in the drainage water was very strong. However the strength of this relationship was dependent on just one or two soils. P losses from a fertile sandy soil were large (1-11 kg ha -1 y - 1 ) throughout the crop rotation and average crop removal (13 kg ha -1 y -1 ) plus the leaching losses were not balanced (average deficit 3-6 kg ha -1 y - 1 ) by the addition of fertilizer, manure or grass compost. No decreasing trend was found in the P losses during seven years. However, the K deficit (average 26 kg ha -1 y -1 ) led to a significant reduction in the leaching trend from this soil. The other soils that had a smaller K deficit showed no significant reduction in the leaching ofK.